No evidence that G6PD deficiency affects the efficacy or safety of daunorubicin in acute lymphoblastic leukemia induction therapy

BACKGROUND/OBJECTIVES

Anthracyclines are used in induction therapy of pediatric acute lymphoblastic leukemia (ALL) and are known to generate oxidative stress; whether this translates into enhanced antileukemic activity or hemolytic effects in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency is unknown.

DESIGN/METHODS

Among 726 pediatric patients with newly diagnosed ALL treated at St. Jude Children's Research Hospital, 22 had deficient G6PD activity. We compared the prevalence of positive minimal residual disease (MRD) ≥1% at Day 15/Day 19 of induction or ≥0.01% at Day 42/Day 46 (end of induction) and the number of red blood cell (RBC) transfusions after daunorubicin in induction between patients with or without G6PD deficiency, adjusting for ALL risk group, treatment protocol, age, and gender.

RESULTS

There was no difference in Day 15/19 (P = 1) or end of induction MRD (P = 0.76) nor in the number of RBC transfusions (P = 0.73); the lack of association with MRD was confirmed in a dataset of 1192 newly diagnosed male patients enrolled in a Children's Oncology Group trial (P = 0.78).

CONCLUSION

We found no evidence that G6PD deficiency affects daunorubicin activity during induction treatment for ALL.

Concordance between glucose-6-phosphate dehydrogenase (G6PD) genotype and phenotype and rasburicase use in patients with hematologic malignancies

Phenotypic rather than genotypic tests remain the gold standard for diagnosing glucose-6-phosphate dehydrogenase (G6PD) deficiency. However, with increasing use of genomic arrays and whole exome or genome sequencing, G6PD genetic data are increasingly available. We examined the utility of G6PD genetic data in patients with hematologic malignancies and the association of G6PD genotype and phenotype with rasburicase-induced methemoglobinemia. We analyzed G6PD activity for 990 patients. Genotype data were available from the Affymetrix DMET array (n=379), whole exome sequencing (n=374), and/or the Illumina exome array (n=634) for 645 patients. Medical records of 341 patients with methemoglobin measures were assessed for the administration of rasburicase. We observed 5 non-synonymous SNPs, 4 of which were known to be associated with deficient G6PD activity (WHO Class I-III). Genotyping 367 males resulted in a positive predictive value of 81.8% (47.8–96.8%), and two males with a Class I-III allele having normal activity both received a red blood cell transfusion prior to the activity assay. However, genotyping males had only 39.1% (20.5–61.2%) sensitivity. Two of the 12 heterozygous females had deficient G6PD activity. Rasburicase-induced methemoglobinemia occurred in 6 patients, 5 of whom had at least one Class I-III allele, despite 2 of these having normal G6PD activity. We conclude that although an apparent nondeficient genotype does not necessarily imply a normal phenotype, a deficient genotype result indicates a deficient phenotype in those without transfusions, and may be a useful adjuct to phenotype to prevent adverse drug reactions.

Genome-Wide Study Links PNPLA3 Variant With Elevated Hepatic Transaminase After Acute Lymphoblastic Leukemia Therapy

Remission induction therapy for acute lymphoblastic leukemia (ALL) includes medications that may cause hepatotoxicity, including asparaginase. We used a genome-wide association study to identify loci associated with elevated alanine transaminase (ALT) levels after induction therapy in children with ALL enrolled on St. Jude Children's Research Hospital (SJCRH) protocols. Germline DNA was genotyped using arrays and exome sequencing. Adjusting for age, body mass index, ancestry, asparaginase preparation, and dosage, the PNPLA3 rs738409 (C>G) I148M variant, previously associated with fatty liver disease risk, had the strongest genetic association with ALT (P = 2.5 × 10^-8 ). The PNPLA3 rs738409 variant explained 3.8% of the variability in ALT, and partly explained race-related differences in ALT. The PNPLA3 rs738409 association was replicated in an independent cohort of 2,285 patients treated on Children's Oncology Group protocol AALL0232 (P = 0.024). This is an example of a pharmacogenetic variant overlapping with a disease risk variant.

Mercaptopurine Ingestion Habits, Red Cell Thioguanine Nucleotide Levels, and Relapse Risk in Children With Acute Lymphoblastic Leukemia: A Report From the Children's Oncology Group Study AALL03N1

Purpose Children with acute lymphoblastic leukemia (ALL) are generally instructed to take mercaptopurine (6-MP) in the evening and without food or dairy products. This study examines the association between 6-MP ingestion habits and 6-MP adherence, red cell thioguanine nucleotide (TGN) levels, and risk of relapse in children with TMPT wild-type genotype. Methods Participants included 441 children with ALL receiving oral 6-MP for maintenance. Adherence was monitored over 48,086 patient-days using the Medication Event Monitoring System; nonadherence was defined as adherence rate < 95%. 6-MP ingestion habits examined included: takes 6-MP with versus never with food, takes 6-MP with versus never with dairy, and takes 6-MP in the evening versus morning versus varying times. Results Median age at study was 6 years (range, 2 to 20 years); 43.8% were nonadherent. Certain 6-MP ingestion habits were associated with nonadherence (taking 6-MP with dairy [odds ratio (OR), 1.9; 95% CI, 1.3 to 2.9; P = .003] and at varying times [OR, 3.4; 95% CI, 1.8 to 6.3; P = .0001]). After adjusting for adherence and other prognosticators, there was no association between 6-MP ingestion habits and relapse risk (6-MP with food: hazard ratio [HR], 0.7; 95% CI, 0.3 to 1.9; P = .5; with dairy: HR, 0.3; 95% CI, 0.07 to 1.5; P = .2; taken in evening/night: HR, 1.1; 95% CI, 0.2 to 7.8; P = .9; at varying times: HR, 0.3; 95% CI, 0.04 to 2.7; P = .3). Among adherent patients, there was no association between red cell TGN levels and taking 6-MP with food versus without (206.1 ± 107.1 v 220.6 ± 121.6; P = .5), with dairy versus without (220.1 ± 87.8 v 216.3 ± 121.3; P =.7), or in the evening/night versus morning/midday versus varying times (218.8 ± 119.7 v 195.5 ± 82.3 v 174.8 ± 93.4; P = .6). Conclusion Commonly practiced restrictions surrounding 6-MP ingestion might not influence outcome but may hinder adherence. Future recommendations regarding 6-MP intake during maintenance therapy for childhood ALL should aim to simplify administration.

Genomewide Approach Validates Thiopurine Methyltransferase Activity Is a Monogenic Pharmacogenomic Trait

We performed a genomewide association study (GWAS) of primary erythrocyte thiopurine S-methyltransferase (TPMT) activity in children with leukemia (n = 1,026). Adjusting for age and ancestry, TPMT was the only gene that reached genomewide significance (top hit rs1142345 or 719A>G; P = 8.6 × 10^-61 ). Additional genetic variants (in addition to the three single-nucleotide polymorphisms [SNPs], rs1800462, rs1800460, and rs1142345, defining TPMT clinical genotype) did not significantly improve classification accuracy for TPMT phenotype. Clinical mercaptopurine tolerability in 839 patients was related to TPMT clinical genotype (P = 2.4 × 10^-11 ). Using 177 lymphoblastoid cell lines (LCLs), there were 251 SNPs ranked higher than the top TPMT SNP (rs1142345; P = 6.8 × 10^-5 ), revealing a limitation of LCLs for pharmacogenomic discovery. In a GWAS, TPMT activity in patients behaves as a monogenic trait, further bolstering the utility of TPMT genetic testing in the clinic.

Systemic Exposure to Thiopurines and Risk of Relapse in Children With Acute Lymphoblastic Leukemia: A Children's Oncology Group Study

IMPORTANCE

Variability in prescribed doses of 6-mercaptopurine (6MP) and lack of adherence to a 6MP treatment regimen could result in intra-individual variability in systemic exposure to 6MP (measured as erythrocyte thioguanine nucleotide [TGN] levels) in children with acute lymphoblastic leukemia (ALL). The effect on relapse risk of this variability is unknown.

OBJECTIVE

To determine the effect of high intra-individual variability of 6MP systemic exposure on relapse risk in children with ALL.

DESIGN, SETTING, AND PARTICIPANTS

We used a prospective longitudinal design (Children's Oncology Group study [COG-AALL03N1]) to monitor 6MP and disease relapse in 742 children with ALL in ambulatory care settings of 94 participating institutions from May 30, 2005, to September 9, 2011. All participants met the following eligibility criteria: (1) diagnosis of ALL at 21 years or younger; (2) first continuous remission in progress at the time of study entry; (3) receiving self-, parent-, or caregiver-administered oral 6MP during maintenance therapy; and (4) completion of at least 6 months of maintenance therapy at the time of study enrollment. The median patient age at diagnosis was 5 years; 68% were boys; and 43% had National Cancer Institute-based high-risk disease.

MAIN OUTCOMES AND MEASURES

Daily 6MP regimen adherence was measured over 68 716 person-days using an electronic system that recorded the date and time of each 6MP bottle opening; adherence rate was defined as the ratio of days that a 6MP bottle was opened to days thata 6MP bottle was prescribed. Average monthly 6MP dose intensity was measured over 120 439 person-days by dividing the number of 6MP doses actually prescribed by the number of planned protocol doses (75 mg/m2/d). Monthly erythrocyte TGN levels (pmol/8 × 108 erythrocytes) were measured over 6 consecutive months per patient (n = 3944 measurements). Using intra-individual coefficients of variation (CV%), patients were classified as having stable (CV% <85th percentile) vs varying (CV% ≥85th percentile) indices. Median follow-up time was 6.7 years from the time of diagnosis.

RESULTS

Adjusting for clinical prognosticators, we found that patients with 6MP nonadherence (mean adherence rate <95%) were at a 2.7-fold increased risk of relapse (95% CI, 1.3-5.6; P = .01) compared with patients with a mean adherence rate of 95% or greater. Among adherers, high intra-individual variability in TGN levels contributed to increased relapse risk (hazard ratio, 4.4; 95% CI, 1.2-15.7; P = .02). Furthermore, adherers with varying TGN levels had varying 6MP dose intensity (odds ratio [OR], 4.5; 95% CI, 1.5-13.4; P = .01) and 6MP drug interruptions (OR, 10.2; 95% CI, 2.2-48.3; P = .003).

CONCLUSIONS AND RELEVANCE

These findings emphasize the need to maximize 6MP regimen adherence and maintain steady thiopurine exposure to minimize relapse in children with ALL.

Inherited NUDT15 variant is a genetic determinant of mercaptopurine intolerance in children with acute lymphoblastic leukemia

PURPOSE

Mercaptopurine (MP) is the mainstay of curative therapy for acute lymphoblastic leukemia (ALL). We performed a genome-wide association study (GWAS) to identify comprehensively the genetic basis of MP intolerance in children with ALL.

PATIENTS AND METHODS

The discovery GWAS and replication cohorts included 657 and 371 children from two prospective clinical trials. MP dose intensity was a marker for drug tolerance and toxicities and was defined as prescribed dose divided by the planned protocol dose during maintenance therapy; its association with genotype was evaluated using a linear mixed-effects model.

RESULTS

MP dose intensity varied by race and ethnicity and was negatively correlated with East Asian genetic ancestry (P < .001). The GWAS revealed two genome-wide significant loci associated with dose intensity: rs1142345 in TPMT (Tyr240Cys, present in *3A and *3C variants; P = 8.6 × 10(-9)) and rs116855232 in NUDT15 (P = 8.8 × 10(-9)), with independent replication. Patients with TT genotype at rs116855232 were exquisitely sensitive to MP, with an average dose intensity of 8.3%, compared with those with TC and CC genotypes, who tolerated 63% and 83.5% of the planned dose, respectively. The NUDT15 variant was most common in East Asians and Hispanics, rare in Europeans, and not observed in Africans, contributing to ancestry-related differences in MP tolerance. Of children homozygous for either TPMT or NUDT15 variants or heterozygous for both, 100% required ≥ 50% MP dose reduction, compared with only 7.7% of others.

CONCLUSION

We describe a germline variant in NUDT15 strongly associated with MP intolerance in childhood ALL, which may have implications for treatment individualization in this disease.

Evidence for age as a modifier of genetic associations for lipid levels

In order to identify novel genetic variants that influence plasma lipid concentrations, we performed a genome-wide association study (GWAS) comprised of 411 children under 18 years of age, ascertained at St. Jude Children's Research Hospital, all of whom were of European, African, or Mexican descent. Promising associations (p < 10(-5)) were subsequently examined in 1040 additional youths and 3508 adults from the Third National Health and Nutrition Examination Survey (NHANES III), a diverse population-based study. Three genotype-phenotype associations replicated in NHANES III youths and three associated in NHANES III adults at p < 0.05; however, no single association was significant in both youths and adults. The most significant association (p= 0.009) in NHANES III youths was between low-density lipoprotein cholesterol (LDL-C) and intronic rs2429917 among participants of African descent. Given the known age dependency of lipid levels, we also tested for gene-age interactions in NHANES III participants across all ages. We identified a significant (p= 0.024) age-dependent association between SGSM2 rs2429917 and LDL-C. This finding illustrates the utility of using children to discover novel variants associated with complex phenotypes and the importance of considering age-dependent genetic effects in association studies of lipid levels.

Asparaginase may influence dexamethasone pharmacokinetics in acute lymphoblastic leukemia

PURPOSE

Dexamethasone is used widely in oncology, but pharmacokinetic studies are lacking. We evaluated dexamethasone pharmacokinetics in children with acute lymphoblastic leukemia.

PATIENTS AND METHODS

We assessed 214 children with acute lymphoblastic leukemia who received 418 courses of oral dexamethasone (8 mg/m(2)/d) on days 1 and 8 of reinduction. Extensive asparaginase use preceded reinduction in the 101 children in the standard/high-risk treatment arm but not in the 113 children in the low-risk treatment arm. A one-compartment model with first-order absorption and disposition was fit to dexamethasone plasma concentrations by using maximum a posteriori probability estimation; we evaluated covariates by using linear mixed models.

RESULTS

Interpatient and intrapatient variabilities in apparent clearance were substantial; they were 46% and 53%, respectively. Variability was explained by the serum albumin concentration (P < .0001), concomitant use of fentanyl (P = .008) and ketoconazole (P = .03), and age (P = .006). Apparent clearance was higher in the low-risk arm (P < .001) and was related to a greater serum albumin concentration (P < .001) and to a lower exposure to asparaginase than in the standard/high-risk arm. Hypoalbuminemia, a biomarker of asparaginase activity, was associated with a lower dexamethasone apparent clearance (P = .04) in patients in the standard/high-risk arm that was more pronounced in those not allergic to asparaginase. Ethnicity or gender did not explain apparent clearance variability.

CONCLUSION

Dexamethasone pharmacokinetics are highly variable and are related to the concurrent use of particular drugs, age, and treatment intensity. Patients allergic to asparaginase may be doubly disadvantaged: they not only suffer from diminished exposure to asparaginase but also, by maintaining high clearance of dexamethasone, may experience fewer antileukemic effects of dexamethasone.

Late-onset delayed excretion of methotrexate

Pleural effusions, ascites, and renal dysfunction decrease the plasma excretion of methotrexate (MTX). However, it is not known what effect these complications have on MTX clearance when they arise after the plasma MTX concentration has fallen to an undetectable level. We describe the clinical course and pharmacokinetics of MTX in a patient with acute lymphoblastic leukemia who experienced pleural effusions, ascites, and renal failure during the weeks after treatment with high-dose MTX (1.63 g/m2 i.v. over 24 h). The patient's normal initial MTX clearance rate (107 ml/min/m2) was consistent with his undetectable plasma level of MTX on day 9 after the infusion. His plasma MTX concentration then gradually increased as his renal function declined, reaching a peak of 0.72 microM on day 15. This unusual finding of an undetectable plasma MTX concentration that subsequently rose to persistent, potentially toxic levels was explained only by a pharmacokinetic model that accounted both for a third space at the time of treatment and for the subsequent decrease in the systemic elimination rate. Therefore, the finding of a physiologic third space during MTX administration combined with the detection of renal dysfunction in the following weeks should be an indication for prolonged therapeutic drug monitoring.

Preponderance of thiopurine S-methyltransferase deficiency and heterozygosity among patients intolerant to mercaptopurine or azathioprine

PURPOSE

To assess thiopurine S-methyltransferase (TPMT) phenotype and genotype in patients who were intolerant to treatment with mercaptopurine (MP) or azathioprine (AZA), and to evaluate their clinical management.

PATIENTS AND METHODS

TPMT phenotype and thiopurine metabolism were assessed in all patients referred between 1994 and 1999 for evaluation of excessive toxicity while receiving MP or AZA. TPMT activity was measured by radiochemical analysis, TPMT genotype was determined by mutation-specific polymerase chain reaction restriction fragment length polymorphism analyses for the TPMT*2, *3A, *3B, and *3C alleles, and thiopurine metabolites were measured by high-performance liquid chromatography.

RESULTS

Of 23 patients evaluated, six had TPMT deficiency (activity < 5 U/mL of packed RBCs [pRBCs]; homozygous mutant), nine had intermediate TPMT activity (5 to 13 U/mL of pRBCs; heterozygotes), and eight had high TPMT activity (> 13.5 U/mL of pRBCs; homozygous wildtype). The 65.2% frequency of TPMT-deficient and heterozygous individuals among these toxic patients is significantly greater than the expected 10% frequency in the general population (P <.001, chi(2)). TPMT phenotype and genotype were concordant in all TPMT-deficient and all homozygous-wildtype patients, whereas five patients with heterozygous phenotypes did not have a TPMT mutation detected. Before thiopurine dosage adjustments, TPMT-deficient patients experienced more frequent hospitalization, more platelet transfusions, and more missed doses of chemotherapy. Hematologic toxicity occurred in more than 90% of patients, whereas hepatotoxicity occurred in six patients (26%). Both patients who presented with only hepatic toxicity had a homozygous-wildtype TPMT phenotype. After adjustment of thiopurine dosages, the TPMT-deficient and heterozygous patients tolerated therapy without acute toxicity.

CONCLUSION

There is a significant (> six-fold) overrepresentation of TPMT deficiency or heterozygosity among patients developing dose-limiting hematopoietic toxicity from therapy containing thiopurines. However, with appropriate dosage adjustments, TPMT-deficient and heterozygous patients can be treated with thiopurines, without acute dose-limiting toxicity.